Query query = em.createQuery("SELECT po.customerId.customerId, MAX(po.shippingCost), 
MIN(po.shippingCost), COUNT(po.orderNum) countligne, 
COUNT(DISTINCT po.productId.productId)\n"   
+"FROM PurchaseOrder po WHERE po.customerId.customerId = :Id
  GROUP BY` po.customerId.customerId");

SELECT t0.CUSTOMER_ID, COUNT(t1.ORDER_NUM), COUNT(DISTINCT(t2.PRODUCT_ID)) 
FROM CUSTOMER t0, PRODUCT  t2, PURCHASE_ORDER t1 WHERE ((t1.CUSTOMER_ID = ?) 
AND ((t0.CUSTOMER_ID = t1.CUSTOMER_ID) AND (t2.PRODUCT_ID = t1.PRODUCT_ID)))
GROUP BY t0.CUSTOMER_ID

..., COUNT(po.orderNum) countligne, ...